1. Field of Invention
The present invention relates to a field of repairing and maintaining transportation infrastructures, and more particularly to a polymer grouting method for uplifting a ballastless track of a high-speed rail.
2. Description of Related Arts
With the steady and sound development of economic constructions, high-speed rail in China is entering a rapid development stage. Since the construction of Qinshen Passenger Railway in 1999, China has built a high-speed railway network which has the largest scale and the highest running speed all over the world by constructing new railways and speeding up conventional railways for over a decade. By the end of December 2012, the high-speed rail which is over 200 km/h is nearly 13,000 km long in China, in which near 3,000 km is by speeding up conventional railways, and the highest running speed designed has reached 350 km/h. According to the National Medium and Long Term Planning Scheme of Railway Network of China, by the end of 2015, 42 passenger-dedicated lines of high-speed railway will be built, and a national high-speed transportation net work will be basically completed, with “four vertical and four horizontal” railways as a skeleton thereof, and a total mileage of more than 15,000 km; by 2020, the mileage of high-speed railway with a speed of more than 200 km/h will be more than 30,000 km in China.
To guarantee the high-speed, safe and smooth running of trains, high-speed rail requires extreme track regularity. If track irregularity degree exceeds design standards, the degree of comfort will be reduced greatly, and even endanger traffic safety if serious, which will inevitably result in slowing down the train speed and restricting the improvement of high-speed rail service. Studies have shown that for trains running at a speed of more than 300 km/h, 10 mm amplitude (wavelengths 40 m) track irregularity will produce in the train continuous vertical vibrations with a frequency of 2 Hz and an acceleration of 1.76 m/s2, which are 3 to 5 times of the specified value by the international vibration environment standard ISO2631 (acceleration of 0.34 to 0.49 m/s2), and this will cause extreme discomfort in the passengers. When traveling at a high speed, track irregularity induced by roadbed settlement will cause huge wheel-rail force and impact force. For example, when a train travels at a speed of 300 km/h, even step-like irregularity on the wheels as tiny as 0.2 mm will produce a 722 kN track rail high-frequency force and a 321 kN low-frequency track rail force, which will accelerate the breaking of track ballast, cause uneven settlement in the roadbed, and may also cause fractures in the rails, wheels and shafts, or cause vicious derailment accidents.
In order to guarantee track regularity, plate ballastless track is commonly used in the construction of modern high-speed rail. The plate ballastless track is a new type of track structure in which the concrete supporting layers, emulsified asphalt cement mortar layers, precast concrete track plates, plate connectors, rail and fasteners are cast-in-place in the roadbed.
Compared with traditional ballasted track, ballastless track structure, without any track sleepers and track bed, and utilizing precast reinforced concrete plates to support the rail directly, has many outstanding advantages such as: good stability and regularity; low building height and light weight that reduces bridge secondary loads and tunnel clearance; slow track deformation and good durability; requiring no maintenance or low maintenance with low costs. Therefore, ballastless track structure has become the mainstream model and the inevitable trend of modern high-speed railway construction, and has been widely utilized in high-speed rail construction of China. More than ten newly built high-speed railways (including passenger-dedicated lines) utilizes ballastless tracks, such as Hada line, Jinghu line, Jingshiwu line, Haqi line, Ninghang passenger-dedicated line, Hebeng passenger-dedicated line, Hangyong line, Zhengxi line and etc.
The advantages of ballastless track are very prominent, but at the same time the ballastless track also requires high quality of basic civil engineering construction, especially high roadbed construction quality. According to the newest High-speed Rail Design Specification (TB 10621-2009), post-construction settlement of ballastless track should not exceed 15 mm (ordinary railway with a design speed of 160 km/h requires no more than 200 mm of post-construction settlement). This strict specification on roadbed settlement deformation of high-speed rail ballastless track has become the main controlling factor to be considered for the design and construction of rail lines.
Due to the vast territory and complex geological conditions of China, a large number of high-speed rail lines have to pass through adverse geological zones such as soft soil, loess, and Karst caves. Therefore roadbed settlement is very common, especially in economically developed areas in China, such as coastal areas, areas near lakes or rivers where soft soil commonly develops. Due to the soft soil has physical and mechanical characteristics of high water content, high compressibility, low strength and low permeability coefficient, when building high-speed railway roadbeds in areas thereof, though necessary sedimentation control measures have been taken, the problems of longer consolidation period and large post-construction settlement deformation are still very serious, which severely affects the long-term stability and regularity of rail tracks, thus become key issues influencing the safe operation of trains and restricting improvement of high-speed rail service performance of China.
For possible roadbed settlement, steel fasteners are pre-provided on high-speed ballastless track to adjust the track deformation. When roadbed settlement causes that vertical linear of the track changes, fasteners can be adjusted to restore the top surface of the track back to elevation designed. However, a maximum adjustment thereof is merely 15 mm. When the roadbed settlement exceeds 15 mm, the sole adjustment of the fasteners can not do anything to help restore the rail alignment.
In areas where roadbed settlement is seriously over standard, the following three measures are generally taken at present. The first measure is to reduce the speed of the train, which is obviously upsetting because the original intention of high-speed rail construction is violated; the second measure is to remove the track and rebuild the roadbed, which causes long-term disruption of the line and extremely high maintenance cost and is thus not normally adopted; the third measure is to reinforce roadbed by grouting or facilitating high-pressure rotary jet grouting piles, so as to improve the bearing capacity and prevent further settlement. Problems mainly existing in the third measure comprises that:                (1) the third measure is only capable of preventing further developing of settlement, but does not help restore existing roadbed settlement to its original design elevation and therefore cannot achieve real “track uplifting”;        (2) the main grouting material is cement-based grout, the slurry consolidation forms rigid bodies in the roadbed, and its modulus of elasticity differs greatly from the roadbed soil, thus producing uncoordinated deformation and inducing cracks and damage;        (3) transportation usually needs to be interrupted, and the railway network operation is affected;        (4) the construction process greatly disturbs the roadbed, and produces large amounts of waste and pollutes the environment;        (5) large construction equipments are used, with a high energy consumption and poor applicability, and has difficulty in entering small sites; and        (6) long construction period is required, with a high material consumption and high cost. As can be seen, there is no effective and practical remediation technology concerning the problem of the ballastless track roadbed settlement, which currently affects the safety operational of China's high-speed railway.        
It is the “bottleneck” restricting the improvement of high-speed rail transportation service performance.
Polymer grouting technology is a rapid foundation reinforcement technology that developed in the 1970s. This technology, by injecting polymeric materials to the foundation and making use of the characteristics of volume expansion of polymeric materials after chemical reaction, reinforces foundation and fills cavities. At present, polymer grouting technology is mainly used for foundation reinforcement and road maintenance in industrial and civil engineering, so far there is no high-speed rail ballastless track uplifting polymer injection method reported.